Plasma display panels of the matrix type are well known in the art. Such panels are described in, for example, U.S. Pat. Nos. 3,681,655; 3,626,244; 3,821,596; 3,993,990 and 4,001,636. Plasma display panels commonly incorporate enclosed panels, gaseous medium, and first and second sets of electrodes. As is known, the gaseous medium can be ionized (charged) or discharged by coupling suitable amplitude signals to corresponding electrodes. The state of the selected cells can be maintained by providing suitable sustaining signals to the associated electrodes. The selection and sustaining operations are explained in the above-mentioned patents.
As sketched in FIG. 1, plasma display panels 11 of the type above, commonly comprise two parallel glass plates 12 and 14 with a plurality of parallel positioned electrode lines 16 and 17 deposited on each inner glass surface with a dielectric material coating on the electrodes. The lines 16 and 17 on each of the panel 12 and 14 are positioned orthogonally in rows "X", and columns "Y" to form a matrix of intersections. The plates 12 and 14 are separated and bonded around the edge to form a cavity which is filled with a neon gas mixture.
Each intersecting point or cell of the matrix, generally labeled 19, is selected to provide a display point by addressing the respective row and column electrodes. The particular cell will then be discharged and the desired data entered therein in response to the input data received from the associated control system 21, as is well known in the art. The cells 19 are addressed or selected, and their selected condition sustained by the "X" sustaining and addressing system 22, and the "Y" sustaining and addressing 23, as is known.
As depicted in FIG. 2, the sustaining or sustainer drive is a differential voltage developed across the X and Y electrode lines. In normal operation, the sustainer drive voltage indicated on the axis of ordinates of FIG. 2 is below the neon gas discharge level required to ignite the panel. The writing operation; that is, data entry into a cell requires two half-select pulses, one on each, of the X and Y matrix electrodes. The two-half select pulses add at the cell or matrix intersection to increase the normal sustainer voltage above the gas discharge level and fire the cell. When the cell ignites, free electrons on the dielectric surface and in the neon gas tend to migrate towards the positive electrode and build a "wall" charge. When a sufficient charge has accumulated, it will neutralize the externally applied voltage and the discharge stops. As shown in FIG. 2, the write pulses are normally added on a base voltage level which minimizes the possibility of other cells firing.
In the normal sequence of operation, the cell fires after the sustain level is reached, the wall charge is built up, and then the cell extinguishes the discharge. On the following negative excursion of the sustainer voltage the wall charge will add to the sustainer voltage and again cause a discharge to occur. Thus, the cell will continue to discharge after the initial write pulse, and will be sustained.
The erase operation requires the wall charge to be removed and the cell returned to its off state. The wall charge can be removed by generating two half-select pulses on each X and Y matrix electrode with a pulse of insufficient pulse width and amplitude to rebuild the wall charge for the next cycle. As mentioned, the half-select pulses are required on the X and Y matrix electrodes to minimize the possibility of other cross-over cells on either line from also writing or erasing.
A plasma panel, as briefly described above can, for certain electrical considerations, be represented as a capacitor with a parallel current generator, representing the neon gas plasma discharge.
Referring to the representative prior art circuit of FIG. 3, a voltage supply V1 providing 195 volts is connected through switch S1 to provide power to a first terminal or plate of capacitor CT (depicting the plasma display panel) and a parallel current generator Id. The other plate of capacitor CT is connected to ground reference. A second power supply V2, providing 60 volts, is connected across a capacitor C1. One terminal of supply V2 and one terminal or plate of capacitor C1 is connected to one side of switch S1, and the other side of switch S1 is connected to capacitor CT. The opposite terminals of power supply V2 and capacitor C1 are connected to one side of a switch S2 and thence to capacitor CT. A third power supply V3 also providing 60 volts, is connected across a capacitor C3. Capacitor C3 is connected in a series circuit with capacitors C1 and C2. One terminal of each of power supply V3, and of capacitor C3 is connected to one side of a switch S3. The other side of switch S3 is connected to the first plate of capacitor CT. As noted, the other plate of capacitor CT connects to ground. A fourth switch S4 connects the ground reference of power supply V1 to the first terminal or plate of capacitor CT; that is, switch S4 shorts capacitor CT to ground.
Note that the switches S1, S2, S3 and S4 indicated in FIGS. 3 and 4 as mechanical switches, represent transistor or IC (integrated chip) switches selectively operated to provide the various operating steps or voltage levels of FIG. 2.
The prior art circuit of FIG. 3 represent a typical method of generating the sustainer drive with a saturated switch at each voltage level. As indicated, this requires three power supplies.